1. Field of the Invention
The present invention relates to an internal combustion-engined tool, in particular, a setting tool for driving in fastening elements and having a drive piston, and a combustion chamber separated by a separation plate with a plurality of through-opening into a fore-chamber section and a main chamber section which adjoins the piston. The present invention further relates to a method of driving the piston and including igniting a combustible gas mixture in the fore-chamber section and producing gas jets which enter the main chamber section through the through-opening of the separation plate.
2. Description of the Prior Act
In the tools described above, the main chamber section adjoins the piston, and the fore-chamber section includes an ignition device for igniting, e.g., an air-fuel gas mixture, whereby gas jets are produced which enter the main chamber section.
The combustion of the air-fuel gas mixture is started in the fore-chamber section with an electrical spark produced by an ignition device. A produced flame front spreads slowly from the center of the fore-chamber section radially outwardly over the volume of the fore-chamber section. The flame front pushes the non-consumed air-fuel gas mixture ahead of itself. The non-consumed air-fuel gas mixture penetrates through the openings in the separation plate into the main chamber section(s), creating there turbulence and a pre-compression. When the flame front reaches the through-openings in the separation plate, the flame enters the main chamber section through the comparative narrow through-openings of the separation plate in accelerated fashion likewise in form of jets, flame jets, creating in the main chamber section further turbulence. The intermixed, turbulent air-fuel gas mixture in the main chamber section is ignited over the entire surface of the flame jets. It burns with a high speed which results in a high efficiency of the combustion as the cooling losses remain small.
In conventional tool, the separation plate has only one row of openings through which the flame can penetrate into the main combustion chamber. The row of openings usually is spaced by a relatively large distance from the ignition device in order to create pre-compression and a sufficient turbulence in the main chamber section. The openings are arranged in a circle concentric with the circular separation plate and the ignition point.
The velocity of the flame front in the fore-chamber section of a conventional tool, because of the laminar flame front, is very low. This results in the following drawbacks:
Because the flame front is laminar and has a low velocity, the time period between the generation of ignition sparks in the fore-chamber section and the start of combustion in the main chamber section is relatively long. This results in relatively high cooling losses, which reduces efficiency.
Because of a slow combustion of the air-fuel gas mixture in the combustion chamber, the pressure in the main chamber section is built up prematurely, resulting in early movement of the piston. To prevent the early movement of the piston, means for retaining the piston need be provided.
Because the through-openings are located far away from the ignition center, a larger portion of the air-fuel gas mixture, which is located in the fore-chamber section, burns out before the flame reaches the openings and ignite the mixture in the main chamber section. Therefore, the largest portion of the combustion of the air-fuel gas mixture in the fore-chamber section does not contribute to energy output and can be considered as a loss or waste.
Accordingly, an object of the present invention is to provide a internal combustion-engined tool of the type described above characterized by a high operational speed and a high efficiency.
Another object of the present invention is to provide a method of driving a piston of an internal combustion-engined tool of the type described above which would insure a high-speed operation of the tool.
These and other objects of the present invention, which will become apparent hereinafter, are achieved by generating gas jets with a predetermined energy by combustion, in the fore-chamber section, at least approximately a volume of a combustible mixture corresponding to the predetermined energy of the gas jets.
In this case, the volume of the combustible mixture, necessary for obtaining gas jets with the predetermined energy, is not combusted in the fore-chamber section in order to immediately produce the gas jets. Therefore, the main chamber section can be ignited relatively early, which increases the operational speed of the tool. Further, because of a relatively small volume of the combustible mixture in the fore-chamber section, the effectiveness of the combustion process increases because for producing the gas jets, there is no need to combust an excessive volume of, e.g., the air-fuel gas mixture. As a combustible mixture, also, oxygen-fuel gas mixture or any other suitable gas mixture can be used.
In accordance with advantageous embodiment of the present invention, the volume of the combustible mixture to be combusted in the fore-chamber section, i.e., the volume necessary for producing the gas jets having a predetermined energy, is determined by the radial distance of the through-openings of the separation plate from the ignition location. At that, the through-openings can be arranged as a row of through-openings located next to each other or can form a circle concentric with the ignition point.
After the ignition of the combustible mixture, a flame front is formed in the fore-chamber section in per se known manner which spreads rather slowly away from the ignition location. After a short period of time, the flame front reaches the openings in the separation plate as the distance of the openings from the ignition point was selected based on only the reduced amount of the combustible mixture which has to be combusted in the fore-chamber section in order to produce, in the main chamber section, the gas jets with a predetermined energy. Therefore, the mixture in the main chamber section is ignited very shortly after the ignition takes place in the fore-chamber section. This substantially reduces the operational cycle of the tool. Despite this, the gas or flame jets in the main chamber section have the necessary predetermined energy to provide, e.g., for a required good turbulence of the combustible mixture in the main chamber section to insure an explosion-like combustion of the combustible mixture in the main chamber section.
In order to increase the turbulence in the main chamber section even more, the arrangement of the through-openings in the separation plate can be so selected that the gas and/or flame jets, which pass through the through-openings, has a direction component extending tangentially to the row of the through-openings.
According to a further particularly advantageous embodiment of the present invention, the combustible gas mixture is fed back from the main chamber section into the fore-chamber section through further through-openings, which sometime are called backstreaming openings, which are provided in a region of the fore-chamber section where the combustible mixture in the fore-chamber section has not yet been combusted after start of the ignition in the main chamber section. This substantially increases the efficiency of the entire combustion process in the combustion chamber.
When the flame jets penetrate into the main chamber section through the first row or set of through-openings in the separation plate, the turbulent combustion, which takes place in the main chamber-section, pushes the non-consumed combustible mixture back into the fore-chamber section through the through-openings in the separation plate which are spaced further away from the ignition point than the through-openings through which flame penetrates into the main chamber section. The gas mixture, which is located further away from the ignition point, is also combusted in a turbulent manner simultaneously with the combustion of the gas mixture in the main chamber section. This insures that the gas mixture portion, which is located in the fore-chamber section further away from the ignition point, also contributes to the piston operation, increasing the total efficiency of combustion.
The backstreaming openings of the separation plate, according to the present invention, can also be so arranged that the backstreaming gas jets, which pass therethrough, also have direction components extending tangentially toward the separation plate that is usually formed as a circular plate.
With respect to a circular separation plate having a first row of through-opening concentric with the separation plate and a second row of backstreaming opening likewise concentric with the separation plate, the following should be pointed out. The first row of through-openings should not be located too close to the ignition point because otherwise not sufficient turbulence would be created in the main chamber section as the flame jets would not have a predetermined level of energy.
On the other hand, the first row of through-openings should not be located too far from the ignition point, because otherwise the ignition in the main chamber section would take place too late, with a too large portion of the combustible gas mixture having been combusted in the fore-chamber section. The diameter of the through-openings of the first row should be small enough in order that the flame and/or gas jets, which enter the main chamber section, are sufficiently strong to swirl the combustible gas mixture filling the main chamber section. However, the diameter of these through-openings should not be too small so that the flame is extinguished. The second row of the through-openings should be located as far as possible from the ignition point, i.e., farther then the first row of through-openings in order that the backstreaming gas jets, from the main chamber section encompasses the largest possible portion of the combustible gas mixture located in the fore-chamber section. Further, the diameter of the through-openings of the second row should, on one hand, be sufficiently small in order that the combustible mixture backstreaming into the fore-chamber section is able to produce a sufficient turbulence in the outer region of the fore-chamber section. On the other hand, the diameter of the through-openings of the second row should be large enough so that the pressure build-up, which is produced by the combustion of the gas mixture located in the outer region of the fore-chamber section, acts in parallel with forces produced in the main chamber section and acting on the piston. Preferably, the backstreaming openings, i.e., the second row openings have a larger diameter than the first row openings.
The present invention is advantageously applicable to tools with a collapsible combustion chamber. In this case, the separation plate and a combustion chamber wall, which limits the fore-chamber section and lies opposite the separation plate, move together in a direction toward the piston when the piston is in its initial, withdrawn position so that the separation plate and the combustion chamber wall lie approximately on each other and/or on the piston. Thereby, the combustion chamber can be freed from residual or waste gases. The expansion of the combustion chamber creates an underpressure which results in suction thereinto of fresh air which is mixed with the fuel gas fed into the combustion chamber before ignition.
Generally, the collapsing of the main chamber section, which results in expulsion of the waste gases, begins only then when the piston has already been brought into its initial position due to the underpressure in the combustion chamber. The provision of the additional row of through-openings in the separation plate provides for a better pressure equalization between the fore-chamber and main chamber sections during cooling down of the waste gases which further facilitate the return movement of the piston into its initial position.
The novel features of the present invention, which are considered as characteristic for the invention, are set forth in the appended claims. The invention itself, however, both as to its construction and its mode of operation, together with additional advantages and objects thereof, will be best understood from the following detailed description of preferred embodiments, when read with reference to the accompanying drawings.